Assessment of Thermo-Treated Bonded Wood Performance: Comparisons among Norway Spruce, Common Ash, and Turkey Oak

Polyvinyl acetate (PVA) exhibits fine adhesion qualities when bonded to wood. However, when using thermo-treated wood, a number of different unstudied factors (such as the water stress condition) influence the wood bonding effectiveness. The main goal of this study was to evaluate how different treatments affect the shear bonding strength for three cases of thermo-vacuum treated woods. Wood from both Norway spruce (Picea abies Karst.) and common ash (Fraxinus excelsior L.) was thermo-treated at 190 °C for two hours under vacuum conditions (250 mbar). Turkey oak (Quercus cerris L.) logs were separately steamed at 110 °C for 24 h, then thermo-vacuum treated at 160 °C for three hours. The bonding shear strength between the PVA adhesive and treated wood was evaluated using water stress condition. The results were compared with the adhesive bond line properties of the untreated wood. The shear strength and wettability of the produced material were measured. Tests for the shear resistance, performed in accordance with the standard DIN EN 204, revealed dissimilar behavior as well as the influence of treatment schedules for the different wood species. Consequently, the tests performed allowed a detailed characterization of the effect of the thermo-vacuum process on the bonding quality of three common woods in different water stress conditions.